There is a massive negative externality for allowing scammers to run free in a situation where the upfront ability to assess fitness-of-goods is lacking.
The cost of dishonesty, therefore, lies not only in
the amount by which the purchaser is cheated; the
cost also must include the loss incurred from
driving legitimate business out of existence.
https://en.wikipedia.org/wiki/The_Market_for_Lemons
the money quote being